1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and a image forming method for effecting a so-called comb-teeth type printing.
2. Description of the Related Art
Among image forming apparatuses which form an image by scanning with an exposure head, it is disclosed an image forming apparatus which exposes an image on an exposure surface by carrying out a so-called xe2x80x9ccomb-teeth type exposurexe2x80x9d (see Japanese Patent Application Publication (JP-B) No. 8-12335). Moreover, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 64-075255, in ink jet recording, there has been known a method in which lines are formed in a backward path between lines recorded in a forward path.
In the image forming apparatus which carries out the comb-teeth type exposure, light emitting elements (not shown) are arranged in the subscanning direction with equal distances therebetween. The first main scanning is carried out such that main scanning lines are main-scanned with fixed distances therebetween. Next, subscanning is carried out at a predetermined feed amount. Further, subsequent main scannings are carried out. As a result, the second or subsequent main scanning lines are sequentially inserted between the first adjacent main scanning lines. The main scanning is repeated for plural times while subscanning at the predetermined feed amount, and a final image is formed.
Hereinafter, a specific explanation will be made with an example for forming an image by an image forming apparatus in which 31 LEDs serving as light emitting elements are arranged with equal distances therebetween.
To form an image by the image forming apparatus, as shown in FIG. 13, the first main scanning lines represented by ▴ are firstly formed on an exposed body such as a photosensitive material or the like. As a result, main scanning lines are formed with all intermittent relative feed direction (subscanning direction) distances between adjacent spot lights (LED lights) being 2xc3x97d.
Then, the exposed body is moved in the subscanning direction by a feed amount of 1=31xc3x97d and is stopped. At this time, second main scanning lines represented by xcex94 are formed.
Further, the exposed body is moved in the subscanning direction by the feed amount 1. At this time, the third main scanning lines represented by xe2x97xaf are formed.
The fourth main scanning lines and subsequent lines are formed as described above.
In this way, an image with the distance between adjacent main scanning lines being d is formed.
In a case of carrying out such comb-teeth type exposure, if the subscanning direction feed amounts do not coincide correctly with each other for each subscanning, specific main scanning lines are close to each other such that a portion of the image corresponding to the lines is made dense. Alternatively, specific main scanning lines are apart such that a portion of the image corresponding to the lines are made fade. That is, irregularities in density is generated periodically on the image.
It is, however, difficult to coincide correctly subscanning direction feed amounts with each other. Accordingly, it is difficult to eliminate the irregularities in density of the image.
Such problems are not limited to a case in which the comb-teeth type exposure is carried out by an image forming apparatus which uses an exposure head. Such problems have also occurred in a case in which a so-called comb-teeth type printing (a method of printing with a recording head as the comb-teeth type exposure) is carried out by an apparatus having a general recording head such as an ink jet printer or the like.
In view of the aforementioned facts, an object of the present invention is to provide an image forming apparatus and an image forming method in which the visibility of irregularities in density is reduced even if there are intermittent relative direction feed amount errors and an image quality is improved.
In accordance with the first aspect of the present invention, an image forming apparatus, wherein each interval of plurality of recording elements provided at a recording head in an intermittent relative feed direction is set such that irregularities in density, generated in an image, due to a feed amount error between a recorded material and the recording head in the intermittent relative feed direction, is generated in an area with a spatial frequency of 1 lp/mm or more, is provided.
If the irregularities in density generated in the image is generated at an area with high spatial frequency, human eyes are difficult to view the irregularities in density. That is to say, in the area with high spatial frequency, even if there is relatively large irregularities in density, the irregularities in density is difficult to be viewed. Accordingly, in accordance with the first aspect of the present invention, the image quality can be improved.
In this specification, the irregularities in density means, for example, density distribution generated due to the difference between density distribution of an ideal image and density distribution of a actual image (between that of desired ideal image and that of actual printed image).
Representative examples of the recorded material and the recording head include an exposure head which exposes scanning light on a photosensitive paper, an ink jet head which ejects ink on an ink jet recording paper, and the like.
For example, in a case of an image forming apparatus having the exposure head which exposes scanning light on the photosensitive paper, recording elements are light emitting elements. The spatial frequency can be almost analyzed for each apparatus type by a subscanning direction feed amount of an exposed body and arrangement positions of the light emitting elements (or corresponding positions of spot lights from respective light emitting elements on the exposed body).
Here, the frequency analysis of the irregularities in density generated by an intermittent relative feed direction (subscanning direction) feed amount error of the exposed body is carried out with arrangement positions of light emitting elements (or the positions of the spot lights on the exposed body) being a parameter. On a basis of the analysis results, the subscanning direction distances between light emitting elements are set such that the irregularities in density is generated at high frequency area with the spatial frequency of at least 1 lp/mm, that is, the irregularities in density is sufficiently suppressed at low frequency area with the spatial frequency of less than 1 lp/mm.
As a result, the image quality of an image subjected to development and the like after exposure can be improved.
In accordance with a second aspect of the present invention, an image forming apparatus, wherein: each interval of plurality of pixels in an intermittent relative feed direction, recorded substantially simultaneously by a plurality of recording elements which are provided at a recording head, is a natural number multiplied by d, wherein a minimum interval of the pixel in the intermittent relative feed direction is d; a feed amount of the intermittent relative feed direction between a recorded material and the recording head is set to be (nxc3x972xc3x97d/k), wherein a number of the recording elements is n, k is a natural number of 2 or more; and assuming that a pixel recorded by i th recording element is recorded on a position of the recorded material, which position is apart from a pixel recorded by a first recording element by a distance Li in the intermittent relative feed direction, each interval of plurality of the recording elements in the intermittent relative feed direction is set such that a pixel is not recorded on a position of the recorded material, which position is apart from the pixel recorded by the first recording element by a distance {Li+jxc3x97(nxc3x972xc3x97d/k)} in the intermittent relative feed direction, wherein j is a natural number, is provided.
The value of k is determined by considering various types of parameters such as a resolution of the image forming apparatus and the like.
The pixel recorded by the i th recording element is recorded on the position of the recorded material which is apart from the pixel recorded by the first recording element in the intermittent relative feed direction by the distance Li, and a pixel is not recorded on the position which is apart from the pixel recorded by the first recording element by the distance {Li+jxc3x97(nxc3x972xc3x97d/k)}. Thus, two pixels are prevented from being recorded on the same position of the recorded material. (Double exposure is prevented.)
For example, in a case of an image forming apparatus having the exposure head which exposes scanning light on the photosensitive paper, the recording elements are the light emitting elements. Assume that the subscanning direction distance (intermittent relative feed direction distance) of any adjacent spot lights which are projected on an exposed body (photo sensitive paper) by the light emitting elements is a natural number multiple of the minimum subscanning direction distance d, the number of light emitting elements is n and k is a natural number of at least 2, the subscanning direction feed amount of the exposed body is set to be (nxc3x972xc3x97d/k). If a spot light formed by the i th light emitting element is projected on a position of the exposed body which is apart from the spot light formed by the first light emitting element in the subscanning direction by the distance Li, the subscanning direction distances between light emitting elements are set such that a spot light is not projected on a position which is apart from the spot light formed by the first light emitting element by the distance {Li+jxc3x97(nxc3x972xc3x97d/k)}.
The spot light formed by the i th light emitting element is projected on a position of the photosensitive paper which is apart from the spot light formed by the first light emitting element by the distance Li. Moreover, a spot light is not projected on a position which is apart from the spot light formed by the first light emitting element by the distance {Li+jxc3x97(nxc3x972xc3x97d/k)}. Thus, two pixels are avoided from being exposed on the same position of the photosensitive paper. (Double exposure is prevented.)
The image forming apparatus may have three, four or five types of the intervals of plurality of pixels in an intermittent relative feed direction. For example, the image forming apparatus may have the intervals, for example, d, 2xc3x97d, 3xc3x97d, 4xc3x97d, 5xc3x97d. Namely, intervals of plurality of pixels in an intermittent relative feed direction includes in this case are five types. Number of types of the intervals is not limited to the same.
In accordance with a third aspect of the present invention, an image forming apparatus according to the first aspect of the second aspect, wherein a plurality of recording element rows, in which each of recording element rows the recording elements are arranged, are provided in a direction substantially perpendicular to the intermittent relative feed direction, is provided.
Therefore, it is possible to form pixels while operations which are different for each recording element row are carried out. For example, in a case of forming a color image with three primary colors of R, G and B, there are three recording element rows for R (red), G (green) and B (blue). Thereby a color image with improved image quality can be formed.
In accordance with a fourth aspect of the present invention, an image forming apparatus according to the third aspect or the fourth aspect, wherein the recording element rows are provided in at least two arrangement patterns, is provided.
Thus, the spatial frequency of the irregularities in density is higher and the irregularities in density is more difficult to be viewed.
In accordance with a fifth aspect of the present invention, an image forming method for forming an image on a recorded material by a comb-teeth type printing by using an image forming apparatus, in which each interval of plurality of recording elements provided at a recording head in an intermittent relative feed direction is set such that irregularities in density, generated in an image, due to a feed amount error between the recorded material and the recording head in the intermittent relative feed direction, is generated in an area with a spatial frequency of 1 lp/mm or more, is provided.
Thus, an image in which quality is improved can be easily formed.
In accordance with a sixth aspect of the present invention, an image forming apparatus according to the second aspect, wherein the first recording element is an element positioned at one end portion of a recording element row in which the plurality of recording elements are arrange, is provided.
In accordance with a seventh aspect of the present invention, an image forming apparatus which forms an image by repeating for a plurality of times a relative movement of a recorded material and a recording portion for recording an image in a subscanning direction at a predetermined amount and a relative movement of the recorded material and the recording portion in the main scanning direction, the image forming apparatus comprising: a plurality of recording elements which are provided at the recording portion and which are arranged in at least one row in the subscanning direction; wherein the plurality of recording elements are arranged with non-uniform interval thereof in the subscanning direction, is provided.
In accordance with an eighth aspect of the present invention, an image forming apparatus according to the seventh aspect, wherein distances, each of which is a distance between the recording elements which are adjacent in the subscanning direction, include at least three types of distances (axc3x97d), (bxc3x97d) and (cxc3x97d), wherein a, b, c are natural numbers which are different from each other, and a minimum interval between adjacent pixels in the subscanning direction is d, is provided.
In accordance with a ninth aspect of the present invention, an image forming apparatus according to the seventh aspect, wherein the plurality of recording elements are arranged in a plurality of recording element rows arranged in the main scanning direction, is provided.
In accordance with a tenth aspect of the present invention, an image forming apparatus according to the ninth aspect, wherein the plurality of recording element rows are provided such that arrangement patterns of at least two recording element rows among the plurality of recording element rows are different, is provided.